OvmfPkg: Update code to be more C11 compliant by using __func__

__FUNCTION__ is a pre-standard extension that gcc and Visual C++ among
others support, while __func__ was standardized in C99.

Since it's more standard, replace __FUNCTION__ with __func__ throughout
OvmfPkg.

Signed-off-by: Rebecca Cran <rebecca@bsdio.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Sunil V L <sunilvl@ventanamicro.com>

OvmfPkg/Library/QemuBootOrderLib/ExtraRootBusMap.c

@@ -227,7 +227,7 @@ CreateExtraRootBusMap (
     DEBUG ((
       DEBUG_VERBOSE,
       "%a: extra bus position 0x%Lx maps to bus number (UID) 0x%x\n",
-      __FUNCTION__,
+      __func__,
       (UINT64)(Idx + 1),
       Acpi->UID
       ));